SPT3 and MOT1 are two yeast genes implicated in the function of the TATA-binding protein (TBP) which are required for normal transcription. They are believed to be functionally related since an spt3 mot1 double mutant is inviable. MOT3 was identified in a screen for high-copy suppressors of this lethality, suggesting that the Mot3 protein is also important for normal TBP function. As genetic analysis demonstrated that Mot3 is not essential for growth, but that loss of function of Mot3 causes mild transcriptional defects in vivo, it is possible that Mot3 is functionally redundant in the cell. The specific aims of this proposal are (1) to investigate the possible functional redundancy of MOT3 by screening for mutations that cause either inviability or strong mutant phenotypes only when in combination with a mot3 mutation and (2) to identify proteins that may physically interact with Mot3 by a two-hybrid screen. These complementary approaches to the study of Mot3 will likely identify factors already known to be important or essential for transcription and/or yet unstudied genes. As transcriptional defects have been implicated in many human disorders such as cancer, and since the transcription process is highly conserved among eukaryotes, results obtained during the course of these studies will be relevant to human health.